The present application is directed to piezoelectric diaphragm structures, and more particularly to poling systems for poling piezoelectric diaphragm structures for optimized diaphragm displacement.
Piezoelectric diaphragm structures are implemented as actuators which move upon being supplied with electrical energy, and as sensors (e.g., pressure, movement, strain sensors) where diaphragm movement is translated into electrical signals. One particular implementation of a diaphragm structure is as part of an ejection unit used to eject drops such as ink, biofluid or other material from a fluid reservoir.
In configuring a piezoelectric diaphragm structure, the ferroelectric ceramics are poled in order to exhibit the piezoelectric characteristics required for operation. Prior to a poling operation, domains of the materials are randomly oriented. During poling, an intense electric field is applied, which may vary dependant on the implementation, but may be in a range of 200 to greater than 15,000 V per millimeter and preferably 1,000 V to 15,000 V. When the field is removed, electric dipoles of the material stay roughly but not completely in alignment. This operation provides the material with a residual polarization.
Presently, such poling operations may occur during fabrication of piezoelectric diaphragm structures. In one operation, the piezoelectric material is poled with an external circuit which is temporarily attached during the manufacturing process. Therefore, the poling operation occurs once, and only during the manufacturing process.
A drawback to this accepted procedure is that over time a piezoelectric material will degrade. This may occur when operation of the piezoelectric diaphragm structures exceed the mechanical, thermal and/or electrical limits of the material, as well as through natural aging. This degrading of the material is particularly acute when highly responsive piezoelectric materials are used. Such highly responsive piezoelectric materials are known to improve the amount of displacement which may be obtained by a diaphragm structure. However, high response materials will also tend to degrade quicker than other piezoelectric materials. In consideration of the above, it is appreciated that once a diaphragm structure is incorporated into a larger device, such as a drop ejection unit, overtime the operational capabilities of the larger devices may degrade due to the decrease or loss in the poling directionality of the piezoelectric material.
The present state of the art does not address this potential degradation of the diaphragm structure in devices that are operating on site in an environment such as an office building, home, factory or other end user's location.